1. Field of the Invention
The present invention relates to an image processing apparatus, image processing method, and a storage medium, and more particularly, to an image processing method which improves a pair of images which are formed to generate a difference corresponding to a parallax of both eyes, an image processing apparatus to which the image processing method is applied, and a storage medium in which a program for realizing the processing method is stored.
2. Description of the Related Art
A stereoscopic image (also called a stereoscopic photograph or a three-dimensional photograph) which can be stereoscopically viewed is composed of a pair of images (still images or video images), which are photographed to generate a difference corresponding to a parallax of both eyes. A stereoscopic effect can be enjoyed by viewing with the naked eye or by means of an instrument such as a viewer. For example, the stereoscopic image can be obtained by photographing the same object at two points having an interval, which is almost equal to or greater than an interval (interocular distance) between the eyes of a person. However, the stereoscopic image can be realized not only by a method using a dedicated camera but also by a simple and low-cost method in which two conventional cameras are arranged. Although this method is currently only known by some users, widespread permeation is a possibility in the future.
On the other hand, an optical image is photoelectrically converted by an image pickup device, and an image signal obtained by the photoelectric conversion is converted into digital data to obtain a digital image. Various methods have been known for reducing noise from the digital image, one example being the following method. That is, an original image is divided into a plurality of small blocks, and template profiles which typically represent image data in the blocks are calculated. Then, the original image data profiles in the blocks are approximated by using the calculated template profiles, and the original data obtained by the approximation are replaced to remove the noise from the image data (refer to, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-144964).
Furthermore, the following method is also used. That is, smoothing and edge detection are performed on an original image data, and mixed image data in which edges and noise of an object are mixed is calculated from the smoothed image data. A weighting coefficient of noise is calculated from an edge strength data calculated by edge detection, and noise data is calculated from the weighting coefficient of noise and the mixed image data. On the other hand, a noise suppression distribution function representing the spread of noise suppression is set, and convolution integral between the function and the noise data is performed to calculate a noise suppression distribution. The noise data is multiplied by the noise suppression distribution to calculate a noise suppression component, the noise suppression component is variably powered to subtract the powered noise suppression component from the image data, thereby suppressing noise (refer to, for example, JP-A No. 2001-285640).
In addition, the following method is also known. That is, for example, an input image signal obtained by photoelectrically reading a film original is decomposed into a high-frequency component and another component to emphasize the high-frequency component. When the film original is at least one of a film in underexposure or a high-speed film, the component other than the high-frequency component is decomposed into two or more components such that the band of the lowest frequency component becomes even narrower, and the frequency component other than the high-frequency component and the lowest-frequency component is suppressed to suppress granulated (noise) (refer to, for example, JP-A No. 11-275350).
The inventors of the present application performed an experiment in which a stereoscopic image photographed by two digital still cameras (DSC) was recorded on a recording material such as a film, and the stereoscopic image was stereoscopically viewed to evaluate the image quality. Results shown that when the right and left images of the stereoscopic image included a difference other than the difference corresponding to a parallax of both eyes, a considerably conspicuous image quality defect was visually recognized when stereoscopically viewing the stereoscopic image.
For example, depending on the characteristics of a CCD incorporated in the DSC as an image pickup device, visible noises were generated in an image photographed by a DSC. The visible noises were generated particularly in high concentration regions (regions with minimal volume of incident light within an entire photographed scene during a photographing state). This noise was not so conspicuous as long as a single image was seen. However, since the noise was random, different noise patterns appeared in the right and left images of the stereoscopic image. When the stereoscopic image in which such noises appeared was stereoscopically viewed, for an appreciator, it appeared that noise patterns were suspended in a space and flicker. The noises were visually conspicuous compared to when a single image was seen.
The above phenomenon is thought to be due to the visual sense of the human being having such characteristics that different regions in the left and right images sensed by both eyes have high sensibilities, and the brain of the appreciator who recognizes the different regions in the left and right images interprets the regions as being polish of a metal or the like based on past experience.
In contrast to this, all of the aforementioned methods of reducing noise from digital images target a single image. Even when the methods are applied to images of a stereoscopic image, it is difficult to reduce or eliminate defects in image quality which are visually conspicuous when the stereoscopic image is stereoscopically viewed.